Laminated strip product for electrical purposes



Sept. 5, 1961 w. J. DAVIS 2,998,840

LAMINATED STRIP PRODUCT FOR ELECTRICAL PURPOSES Filed Feb. 28. 1957United States Patent C) ice 2,998,840 LAMINATED SI RH PRODUCT FORELECTRICAL PURPOSES William J. Davis, West Reading, Pa., assignor to ThePolymer Corporation, Reading, Pa., a corporation of Pennsylvania FiledFeb. 28, 1957, Ser. No. 643,002 Claims. (Cl. 154-2.6)

This invention relates to a composite or laminated strip or tape-likeproduct for use in electrical devices and equipment. The invention isespecially concerned with a composite strip or tape structure as a stockprodnot which is adapted for a variety of uses in the electrical andelectronic arts, as will further appear.

One of the principal objects of the present invention is the provisionof a composite strip stock product having both electrical and magneticproperties or characteristics.

A further object of the invention is the provision of a stock product ofthe kind above mentioned and fur.- ther having specially advantageousphysical characteristics including a high degree of flexibility, theproduct, in fact, having a striking limpness which makes it very easy towind upon other elements or upon itself. Moreover, the product may evenbe sharply bent or creased without impairing either the electrical ormagnetic properties thereof.

Other objects of the invention and other advantageous characteristics ofthe product can be explained more readily after more detailedconsideration of the structure of the product, for which purposereference is made to the accompanying drawing, in which FIGURE 1 is aperspective view of a portion of strip stock made up according to thepresent invention;

FIGURE 2 is a view similar to FIGURE 1 but illustrating a modification;

FIGURE 3is a somewhat diagrammatic illustration of one type ofelectrical device made up .by use of the product of the presentinvention; and

FIGURE 4'is a view of another device for which the product of theinvention is well adapted.

Before describing the features illustrated in the drawing, it is herefirst pointed out that the present invention contemplates employment offinely divided ferromagnetic material as a magnetic constituent of theproduct. Use of finely divided ferromagnetic materials for variousmagnetic purposes, especially where high frequency currents areinvolved, is already known. In accordance with the present invention,however, such material is employed in a new way and in a specialrelationship to other components of the composite structure.

As seen in FIGURE 1, a strip stock product is made up of two strip ortape-like elements shown at 5 and 6. Element 5 comprisespolytetrafiuoroethylene having finely divided particles of ferromagneticmaterial dispersed therein. Preferably, according to the invention, theferromagnetic materials have both magnetic and electrically conductiveproperties or characteristics, for instance, carbonyl iron. Moreover,for some special uses a strip product construpted according to theinvention may be made up with tape 5 containing dispersed particles ofelectrically conductive substantially nonmagnetic material.

For most purposes it is advantageous to employ relatively highpercentages of the ferromagnetic material, preferably upward of 50% byvolume of the total material of which the strip 5 is formed. Especiallydesirable characteristics are obtained for many purposes where the strip5 comprises upwards of about 85% ferromagnetic material, the balancebeing polytetrafiuoro- 2,998,840 Patented Sept. 5, 1961 ethylene. Amethod for preparing an intimate intermixture of ferromagnetic materialand polytetrafluoroethylene in percentages running up even to about 98%or 99% by volume of the ferromagnetic material is disclosed in mycopending application Serial No. 495,456, filed March 21, 1955. Thedetails of that method need not be considered herein, although it ishere mentioned that the intimate admixture of the ferromagnetic materialand the polytetrafluoroethylene in fine particle form obtainableaccording to the method of the application above identified may beformed under pressure into various shape-retaining structures. Forexample it may be extruded under pressure in the form of a rod. It mayalso be calendered to form thin strips, such as that illustrated at 5 inFIGURE 1. In an alternative procedure for producing a tape or strip, arod may first be extruded, and then the rod rolled to flat shape.

Strip stock according to the invention may be made up either of sinteredor unsintered tape.

Filled polytetrafiuoroethylene strip or tape prepared as above mentionedhas considerable strength even in the green state, but the strength isextensively increased by sintering the strip, for instance by heating,preferably in an inert atmosphere at a temperature of from about 627 F.to about 800 F.

The other component of the composite structure as shown in FIGURE 1,i.e., the strip 6 comprises an electrically conductive element bonded toone side of the strip 5 The element 6 is advantageously of thin orfoil-type metal and is desirably highly flexible, so that the laminatedstructure retains a high degree of flexibility. The conductive element 6may for example comprise a separately formed aluminum or other metalfoil adhesively bonded to one face of the strip 5. As an alternative, aconductive type of aluminum paint or coating composition may be appliedto one face of the strip 5 in order to provide a thin conductive elementbonded to the strip 5. Still another eifective technique in pro- Vidingthe conductive element bonded to the strip 5 is the use of vacuummetalizing methods of well-known types. It will be appreciated that inthe illustration of FIGURE 1, although the width of the strip stockthere shown is suitable in preparing a strip stock product according tothe invention, ordinarily the conductive element 6 would be much thinnerthan shown, the thickness being exaggerated purely for the sake ofillustration. Similarly, for most purposes the strip 5 would be thinnerthan appears in FIGURE '1, although in some cases relatively thick tapeor strip may be used.

The strip stock of FIGURE 1 may be produced in any length desired, orcontinuously, and pieces may thereafter be cut from a stock roll inorder to fill desired specific needs in fabricating electrical devicesor other equipment therefrom.

When the filled polytetrafluoroethylene strip is to be sintered, it ispreferred that the conductive element or elements be applied or bondedto the poly-tetralluoroethylene strip subsequent to the sinteringoperation, which operation requires relatively high temperatures, asalready mentioned, which in many cases would adversely influence thebondingof the conductive strip.

In a composite structure such as shown in FIGURE 1, the strip 5contributes magnetic properties by virtue of the ferromagnetic particlesdispersed therein. In addition, strip 5 further contributes dielectricproperties, by virtue of the presence of the polytetrafiuoroethylene,and this strip constitutes a nonconductive element which, in use, forinstance when the composite strip is wound upon itself, acts to insulateone turn from another. When employing electrically conductiveferromagnetic material as the filler in the strip 5, as is preferred, itis also preferred to insulatively coat the individual particles of thefiller prior to incorporation thereof in the strip. This may beaccomplished by applying a phosphate coating, as is mentioned in mycopending application above identified. The use of conductive particleswith insulating coatings further enhances the dielectric properties ofstrip 5.

Although the conductive strip 6 may be of width diiferent from that ofstrip 5, either narrower or wider, the embodiment as illustrated inFIGURE 1 wherein the strips and 6 are of the same width is preferred forsome purposes. However it is preferred for most put poses that theconductive strip should be at least slightly narrower than the strip 5.

In FIGURE 2 there is illustrated a modification in which a strip 5a isidentical with strip 5 described above in connection with FIGURE 1 InFIGURE 2, however, instead of a single conductive strip, two conductivestrips 6a and 6b are bonded to strip 511. Strips 6a and 6b extendthroughout the length of strip 5a but are transversely spaced from eachother." More than two conductive strips could also be used for specificpurposes. An example of a special use for the embodiment of FIGURE 2 ismentioned hereinafter.

In FIGURE 3 there is illustrated a device made up of strip stock of thetype shown in FIGURE 1'. Here two pieces of the composite strip materialare superimposed upon one another and the assembly is then spirallywound end-wise thereof. Electrical connections 7 and 8 are associatedwith the outer ends of the conductive elements 6 of the two strips, andconnections 9 and 10 are associated with the inner ends of the twoconductive strips. With a device formed in this way, and withappropriate coupling of the connections 7, 8, 9 and 10, both capacitanceand inductance may be introduced into a circuit. The high degree offlexibility of the strip stock of the invention is an importantcharacteristic in enabling the production of a unit such as shown inFIGURE 3'. In this connection, a device of the kind illustrated inFIGURE 3 would for most purposes desirably be wound much more tightlythan indicated in the figure. Indeed, the device may readily be wound orWrapped so that all of the turns directly contact each other, theshowing of spacing between the turns in FIGURE 3 being merely forconvenience and clarity of illustration. With a device made up in thismanner, the capacitance of the unit and also the inductance of the unitare increased at least several times as compared with a similar unitmade up of conductive strips and interleaved dielectric layers in whichthe latter do not incorporate the ferromagnetic material.

A strip stock product of the kind shown in FIGURE 2 may be used informing a device similar to that shown in FIGURE 3. In this case twoadjacent ends ofeach of the pairs of conductive strips'6a and 6b may beinterconnected, the electrical connections being made at the oppositeends, in this way providing for doubling the conductor path through theunit. Also, the strips 611 and 6b may be maintained in electricallyseparated circuits or interconnected in various other ways for theaccomplishment of different electrical or electro-magnetic efiects.

Another illustrative use of the strip stock product of the presentinvention is shown in FIGURE 4. This shows a delay line incorporating acentral dielectric core 11 with a spirally wound conductor 12 thereon.This is covered by strip stock of the kind shown in FIGURE 1 spirallywound about the spiral conductor 12, with the ferromagnetic strip 5 ofthe composite tape adjacent to the conductor 12. When wound in' this waythe conductive ele ment 6 of the composite tape forms a shield or secondconductor which is both inductively and capacitatively coupled with theconductor 12. By simple winding of the composite tape in spiral fashionabout the conductor 12, the turns of the conductor 6 while efifectivelyshielding the entire cable structure, are at the same time insulatedfrom each other, so that the conductor 6 has an extended spiral patharound the cable. The entire assembly may be covered with a simple typeof electrical insulating tape such as indicated at 13, or other similarflexible covering which aflords mechanical protection.

When a delay line of this type or a similar structure is made up of acore of flexible material, for instance of polytetrafluoroethylene, withor without ferromagnetic particles dispersed therein, the structure ischaracterized by a high degree of flexibility, so that it may readily becoiled or even bent upon itself without adversely influencing eitherelectrical or magnetic properties.

It is to be understood that the foregoing description and theaccompanying drawings are illustrative of the invention and'are not tobe taken as limiting the scope of the appended claims.

I claim: 7

1. As a strip stock product, a laminated structure comprising anelectrically conductive flexible metallic foiltype strip extendedlengthwise of and bonded to one side of a flexible non-conductive tapecomposed of polytetrafluoroethylene having finely divided particles ofmag-.

netic material dispersed therein.

2. As a strip stock product, a laminated structure comprising anelectrically conductive flexible metallic foiltype strip extendedlengthwise of and bonded to one side of a flexible non-conductive tapecomposed of polytetrafluoroethylene having finely divided particles ofan electrically conductive ferromagnetic material dispersed therein.

3. As a strip stock product, a laminated structure comprising a flexiblenon-conductive tape composed of polytetrafluoroethylene having finelydivided particles of magnetic material dispersed therein, and aplurality of electrically conductive flexible metallic foil-type stripsbonded to one side of said tape in spaced parallel relation runninglengthwise of said tape.

4. As a strip stock product, a laminated structure comprising anelectrically conductive flexible metallic foiltype strip extendedlengthwise of and bonded to one side of a flexible non-conductive tapecomposed of sintered polytetrafluoroethylene having finely dividedparticles of magnetic material dispersed therein.

5. A method for making a strip stock product for use in electricalequipment, which method comprises pressure compacting in the form of atape intermixed particles of polytetrafluoroethylene and a finelydivided filler comprising a magnetic material, sintering the tape, andthereafter bonding to one side of the tape an electrically conductiveflexible metallic foil-type strip in position to extend lengthwise ofthe tape.

References Citedin the file of this patent UNITED STATES PATENTS2,427,183 Berry Sept. 9, 1947 2,484,483 Berry Oct. 11, 1949 2,520,173Sanders Aug. 29, 1950 2,638,523 Rubin May 12, 1953 2,691,814 Tait Oct.19, 1954 2,849,312 Peterman Aug. 26, 1958

